The chemicals presently used for weed control in wheat or barley either control wild oats or broadleaf weeds but none of them adequately control both broadleaves and wild oats. For example, the commercial herbicide, BROMINIL ##STR2## and 2,4-D control broadleaf weeds but not wild oats, whereas the commercial herbicide, CARBYNE CONTROLS WILD OATS EFFECTIVELY BUT DOES NOT ADEQUATELY CONTROL BROADLEAVED PLANTS.
5-Hydroxy-2-pyridine carboxylic acid and the methyl ester (of the carboxyl group) are known compounds, but no reference to the amide or to any brominated derivatives of any of these compounds has been found in the literature.
U.S. Pat. No. 3,651,070 discloses several specific compounds of the formula ##STR3## WHERE X is halogen, n is 1 or 2 and R is like or unlike radicals of the carboxylate group, including acids, salts and esters thereof. The disclosed species are said to have utility as herbicides, bactericides and fungicides. Among these, the closest compound to those of the present invention is trichloro-4-hydroxypicolinic acid. No compounds in which X is other than chlorine or in which R is --CONH.sub.2 are disclosed. The only pertinent activity data given is for applications of the above-named compound, as such and as the potassium salt, at a level of at least 64 lbs. per acre to tomatoes, beans, corn, and oats. Complete plant kill only of tomatoes is reported.
The compound 3,5-diiodo-4-hydroxybenzamide is reported (Cooke et al; Proc. Northeast Weed Control Conf., 19, 321-3 (1965)) to be inactive and 3,5-dibromo-4-hydroxybenzonitrile is shown to be less active than 3,5-diiodo-4-hydroxybenzonitrile.